How does getchar() work for Serial Communication?

For serial communication programming,
can I simply use getchar() as in CSample
or do I have to use interrupt-driven
one as in INTSIO? What is the difference
between these 2 sample projects?

In CSample, the serial port interrupt is
even not enabled(?), so I wonder if it
can really capture input stream from serial port, or it justs simulate keyboard input as serial port.

If I use interrupt, can I bypass getchar(), and check the serial buffer directly?

Can anybody please tell me what is the
function of getchar() in serial port
programming and how to correctly use it?

I am a beginner of C51 development, any
comments will be greatly appreciated.

Thanks.